This invention relates generally to fluid systems for internal combustion engines, and more particularly to a high pressure rail assembly of a fuel system of an internal combustion engine.
Two common types of fuel systems for internal combustion engines include hydraulically-actuated-electronically-controlled unit injector type fuel systems and common rail type fuel systems. In some hydraulically-actuated-electronically-controlled unit injector type fuel system, working fluid, such as hydraulic oil, is supplied from a high pressure pump to two high pressure rails or collection chambers. The high pressure rails are connected to the fuel injectors of the fuel system and deliver the high pressure working fluid to a fuel injector upon actuation of the injector. The high pressure working fluid enters the fuel injectors and urges an intensifier piston of the injector to pressurize fuel located in a fuel chamber of the fuel injector. The pressurized fuel then exits the tip of the injector into a combustion chamber of the engine. U.S. Pat. No. 5,168,855 to Dwight V. Stone discloses a hydraulically-actuated-electronically-controlled unit injector type fuel system including two high pressure rails.
Similar to the hydraulically-actuated-electronically-controlled unit injector type fuel systems, some common rail fuel systems include two high pressure rails supplying working fluid to the fuel injectors. In this system, however, the working fluid is pressurized fuel. Accordingly, the fuel injectors do not include an intensifier piston, but rather perform essentially as a gate for supplying the pressurized fuel from the high pressure rails to the combustion chambers of the engine.
Maintaining the pressure of the fluid in the high pressure rails as constant as possible is a requirement for efficient engine operation of both the hydraulically-actuated-electronically-controlled unit injector and common rail type fuel systems. The amount of fuel that is injected into a combustion chamber by a fuel injector is directly dependent on the pressure of the working fluid in the high pressure rails. Accordingly, pressure fluctuations in the high pressure rails can cause the fuel injector to inject more or less fuel than is needed by the engine, thus detrimentally affecting engine performance.
One problem in maintaining consistent fluid pressure in the high pressure rail is the fact that each injection event inherently causes a quick drop in the fluid pressure of a high pressure rail because working fluid from the rail quickly exits the rail and flows into a fuel injector. Even further, the pressure fluctuations caused by one injection event can join with pressure fluctuations caused by previous or subsequent injection events to intensify the pressure fluctuations. Further, these pressure fluctuations may include peak pressures that can stress the components of the high pressure rail and thereby affect the design requirements of the fuel system.
U.S. Pat. No. 5,168,855 provides a system that reduces pressure fluctuations in a hydraulically-actuated-electronically-controlled unit injector type fuel system having two high pressure fluid rails. The ""855 patent discloses one high pressure rail on each side of the engine. A Helmholz resonance isolation type valve is located in the lines connecting each high pressure rail to a high pressure pump. The Helmholz resonance isolation type valve includes a one-way check valve and an orifice in parallel flow communication. The Helmholz type valve acts to limit pressure fluctuations from flowing from one high pressure rail to the other high pressure rail. One drawback feature of the fuel system of the ""855 patent is that the pressure fluctuations caused by a fuel injector on one side of the engine are not isolated from the other injectors located on the same side of the engine.
The present invention provides a fuel system for an internal combustion engine that avoids some or all of the aforesaid shortcomings in the prior art.
In accordance with one aspect of the invention, a fuel system for an internal combustion engine includes at least four fuel injectors for supplying fuel to corresponding combustion chambers of the engine, and a pump in fluid communication with the fuel injectors and supplying working fluid to the fuel injectors. The fuel system further includes at least three high pressure rails fluidly connected between the pump and the at least four fuel injectors.
According to another aspect of the present invention, a method for reducing pressure fluctuations in a fuel system of an internal combustion engine includes supplying working fluid from a high pressure pump to at least three high pressure rails, and supplying fuel injectors of the engine with working fluid from the at least three high pressure rails.
According to yet another aspect of the present invention, a method for supplying working fluid to a group of fluid control valves of an internal combustion engine includes supplying working fluid from a high pressure pump to at least a first, second and third high pressure rail. The method further includes passing working fluid from the first high pressure rail through a fluid control valve of a first group of fluid control valves, passing working fluid from the second high pressure rail through a fluid control valve of a second group of fluid control valves after said passing of working fluid through a fluid control valve of the first group of fluid control valves, and passing working fluid from the third high pressure rail through a fluid control valve of a third group of fluid control valves after said passing of working fluid through a fluid control valve of the second group of fluid control valves.